10:30
Session 1B: Working fluids
Chair: Andrea Spinelli
10:30
20 mins
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Performance Analysis of a Revolving Vane Expander in an Organic Rankine Cycle with Hydrofluoroolefins (HFOs) in Place of R134a
Ali Naseri, Stuart Norris, Alison Subiantoro
Abstract: The Organic Rankine Cycle (ORC) is a promising method to exploit low to medium temperature heat sources. Though it is a mature technology, the selection, sizing and optimisation of the expander used to extract energy is still an active topic of research since it can strongly affect the performance of the ORC. Among the types of volumetric expanders, the use of rotary vane expanders is advantageous, particularly in small-scale applications, due to their simplicity, low manufacturing and maintenance cost, low noise, and high volumetric expansion ratios. However, they generally perform poorly in comparison to other rotary machines because of their inevitable leakage and friction losses, leading to low isentropic efficiencies. A Revolving Vane (RV) expander, in which both the rotor and cylinder rotate, unlike conventional vane-type mechanisms, has been shown to exhibit a significant reduction in friction losses [1]. Such a machine has been previously studied in compressed air and refrigeration systems, but not in an ORC system.
In this study, the first law of thermodynamics is used to evaluate the performance of a Revolving Vane expander within an ORC system using R1234yf and R1234ze(E). These fluids are popular replacements for R134a, since they have low global warming and zero ozone depletion potentials. Previously developed mathematical models of the RV expander [1, 2] have been adopted for the study. Various operating conditions are simulated to find the optimal performance parameters of the expander using the chosen working fluids. The results demonstrate the potential of the RV expander for small-scale ORC applications. Moreover, the characteristics of the expander at various operating conditions are observed, showing that the expander design is suitable for small-scale ORC applications.
Reference
1. Subiantoro, A. and K.T. Ooi, Comparison and performance analysis of the novel revolving vane expander design variants in low and medium pressure applications. Energy, 2014. 78: p. 747-757.
2. Subiantoro, A. and K.T. Ooi, Analysis of the Revolving Vane (RV-0) expander, part 2: Verifications of theoretical models. International Journal of Refrigeration, 2012. 35(6): p. 1744-1756.
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10:50
20 mins
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Performance Prediction and Design Optimization of a kW-size Reciprocating Piston Expander Working with Low-GWP Fluids
Maria Alessandra Ancona, Michele Bianchi, Lisa Branchini, Andrea De Pascale, Francesco Melino, Saverio Ottaviano, Antonio Peretto, Noemi Torricelli
Abstract: Micro-ORC systems represent a promising technology in the field of the energy conversion from low-grade temperature sources. However, nowadays the working efficiency are still relatively low, resulting from the lack of appropriate expander machines but also from the need of optimal working fluid. The ideal working fluid should maximize the performance of the system for given operating conditions (as the hot source temperature) and, at the same time, it must respect the environmental impact restrictions, linked to the fluid ozone depletion potential (ODP) and global warming potential (GWP). In this study, low-GWP fluids, as R1234yf and R1234ze(E) have been compared with R134a, as working fluid of a kW-size reciprocating piston expander and the optimization of the built-in volume ratio has been performed for each analyzed fluid in design conditions. To this purpose, a previously calibrated and validated semi-empirical model of the expander has been integrated with a new gear pump model, in order to simulate the volumetric machines into the real operation of the ORC system. The comprehensive model is conceived to accommodate the change of the working fluid: model parameters taking into account the thermo-fluid-dynamic properties of the fluid are updated compared to the original values calibrated over R134a by means of an extensive experimental campaign.
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11:10
20 mins
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Equation-based Model for Simultaneous Working Fluid - Process - Heat Integration Optimization of Organic Rankine Cycle for Liquefied Natural Gas regasification
Yingzong Liang, Zhi Yang, Jianyong Chen, Xianglong Luo, Ying Chen
Abstract: The organic Rankine cycle (ORC) is a promising energy recovery technology that finds application in a variety of energy sources due to its exceptional flexibility to operate for a wide temperature range [1]. Among different energy sources, liquefied natural gas (LNG) is a great candidate because of its low temperature (110 K), which can significantly increase the efficiency of low grade heat recovery (<373 K). Its massive heat requirement (tens of MW) during regasification also guarantees a substantial energy output [2].
Despite its great potential, design of the Organic Rankine Cycle for LNG regasification is extremely challenging due to the complexity of the problem, which must consider process design, heat integration, and composition of its working fluid at the same time. Usually, optimization of the aforementioned problem is formulated as a mixed-integer nonlinear programming (MINLP) problem. However, the optimization problem is computationally expensive due to the large number of binary variables used to model heat integration and heat capacity variation of process streams during temperature exchange [3]. Exacerbating the problem is the use of oversimplified thermodynamics embedded in the model, which can make the results inaccurate since the thermodynamics used is not rigorous.
In this paper, an equation-oriented model is developed for simultaneous process-heat integration-working fluid optimization of LNG regasification process using ORC for cold energy recovery. To address the computational difficulties, we present a novel formulation approach for heat integration that significantly reduces binary variables compared with conventional formulation. Additionally, an efficient modeling method is proposed to accommodate the heat capacity change of streams as a result of phase change during heat exchange. We also integrate a rigorous thermodynamics module based on SRK equation of state in our model to ensure accurate computation of thermodynamics properties (e.g. vapor-liquid equilibrium and enthalpy) so that the composition of the work fluid can be optimized. Thanks to the efficient formulation and rigorous thermodynamics calculation, our model is capable of solving the solving the simultaneous optimization problem effectively. Simple examples are presented to illustrate the proposed model, then a LNG regasification process design problem is used to demonstrate the efficiency the proposed model.
References
[1] Tchanche BF, Lambrinos G, Frangoudakis A, Papadakis G. Low-grade heat conversion into power using organic Rankine cycles–A review of various applications. Renewable and Sustainable Energy Reviews 2011;15:3963-79.
[2] Gómez MR, Garcia RF, Gómez JR, Carril JC. Review of thermal cycles exploiting the exergy of liquefied natural gas in the regasification process. Renewable and Sustainable Energy Reviews 2014;38:781-95.
[3] Kamath RS, Biegler LT, Grossmann IE. Modeling multistream heat exchangers with and without phase changes for simultaneous optimization and heat integration. AIChE J 2012;58:190-204.
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11:30
20 mins
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Thermodynamic Selection of the Optimal Working Fluid
Attila R. Imre, Réka Kustán, Axel Groniewsky
Abstract: Using a recently proposed novel working fluid classification scheme based on the entropy-sequences of various characteristic point on the temperature-entropy curves [1], we are proposing a method to select the thermodynamically most suitable working fluid for a given heat source. The maximal and minimal temperatures of the potentially usable ORC are determined by the temperature of the heat source (high-temperature reservoir), the temperature of the environment (low-temperature reservoir) and the pinch point temperature differences. Using these data, we are able to select a working fluid (from a database [2]), with an ideal adiabatic (isentropic) expansion step starting from a saturated vapour state and terminating also in a saturated vapour state (or at least in the vicinity of this state). In this way, one can use the most simple ORC layout, using only a pump, a fluid heater, an evaporator, an expander, and a condenser, avoiding the use of superheater (or droplet separator) and recuperator. Since the fluid is always in dry condition during expansion, droplet erosion can also be avoided.
Presently we have a database of 30 pure fluids with T-s data taken from the NIST Chemistry Webbook. Most of these fluids were termed formerly as “dry”, while in the novel classification they are in various isentropic sub-classes, namely in ANCMZ, ACNMZ. ANZCM and ANCZM. From the present working fluid set, one can choose the thermodynamically most suitable cryogenic cycles, but after proper expansion, the database will be available for other temperature ranges (like geothermal or waste heat applications).
[1] G. Györke, U. K. Deiters, A. Groniewsky, I. Lassu, A. R. Imre: Novel Classification of Pure Working Fluids for Organic Rankine Cycle, Energy, 145 (2018) 288-300.
[2] G. Györke, A. Groniewsky, A. R. Imre: A simple method to find new dry and isentropic working fluids for Organic Rankine Cycle, Energies, 12 (2019) 480.
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11:50
20 mins
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Influence of the Use of a Nanonfluid on Net Power Production in ORCs for Low-grade Waste Heat Recovery Applications
Giovanna Cavazzini, Serena Bari, Vittoria Benedetti, Peter McGrail, Giorgio Pavesi, Guido Ardizzon
Abstract: In the industrial sector, medium, low and ultra-low temperature waste heat represents a significant source of energy loss as well as constitutes a harmful environmental effect, which must be avoided. Nonetheless, waste heat could represent a free and vast potential when a technology to recover effectively energy at low temperatures is utilized.
In this context, the Organic Rankine Cycle (ORC) technology is a proven solution because, being the working fluid an organic substance with low boiling temperature, it is more suitable than water when low grade heat needs to be recovered.
However, the recovery process presents several challenges when dealing with low and ultra-low temperature heat sources (<150°C) and one of the most significant is the proper choice of the working fluid. In such a context, numerous studies have been already carried out to identify in each particular application the working fluid that overperformed the others, but at low grade heat source temperatures organic working fluids showed similar decaying performances with thermal efficiencies typically ranging from 8 to 10%.
So, the identification of a working fluid, performing significantly better than the others, is still far from being achieved, due to difficulty in the maximization of the heat transfer from low grade heat sources. To achieve higher heat transfer efficiencies, unconventional working fluids with enhanced thermal properties should also be investigated. Regarding this topic, nanofluids, suspensions of nanoparticles in a base fluid, synthesized intentionally to have enhanced thermal properties, might have the potential to increase ORCs efficiency.
This paper presents a more in-depth investigation of the applications of this particular type of nanofluids in the ORC field, developing a numerical model for assessing the nanofluid gain in terms of net power production. In particular, the possible combination of the base fluid R245fa with the nanoparticle MIL101, a robust Metal Organic Heat Carrier, is considered.
Thermo-physical models have been used to predict the nanofluids behaviour in different operative conditions of the ORC plant. Therefore, in order to limit the influence of the model uncertainties on the results of the numerical analysis preliminary experimental analyses are carried out to assess the adsorption behaviour of MIL101 in R245fa. The resulting performance of the MIL101/R245fa is then compared with those of pure organic fluids, whose cycle is optimized in order to maximize the power output.
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